The invention concerns a polymerization apparatus for finishing high viscosity synthetic condensation polymers. More particularly, it concerns an apparatus having vertical rotating screw elements which fully wipe the interior surfaces of the finisher apparatus.
U.S. Pat. No. 3,717,330 issued to Pinney describes a separator-finisher apparatus suitable for use in the production of synthetic condensation polymers such as polyamides and polyesters. The apparatus disclosed in the patent includes a vessel having an interior surface throughout its vertical length in the shape of two intersecting conical frustums with parallel and substantially vertical axes, the bases of the frustums being displaced upwards with respect to the apexes, two interengaging helical screw elements rotatably mounted within the vessel which upon co-rotation conform to the interior surface of the vessel such that the screw elements effect a complete wiping of the interior surface of the vessel, and the screw elements interengage each other uninterruptedly along their lengths such that each element effects a complete wiping of an adjacent element. The entire disclosure of the Pinney patent is incorporated herein by way of reference.
When such an apparatus is used for the preparation of polymers, such as poly(hexamethylene adipamide), which are particularly susceptible to thermal degradation and gelation in stagnant regions of a processing vessel, it is particularly desirable to continuously supply fresh polymer to all the wiped surfaces. In so doing, care should be taken to avoid undue splashing which results in the generation of suspended molten polymer particles (aerosols) which can be carried out of a vent and create deposition problems in a venting system. Because of the vertical arrangement of any such apparatus, special care should be taken to supply fresh polymer to the top inner surface during use. This not only utilizes the maximum surface area for promoting reaction, but also prevents stagnation and polymer degradation on this surface.
The present invention provides an improvement in the apparatus of the type described in the Pinney patent. More particularly, it provides a modification of the upper ends of the screw elements which enhances their ability to carry fresh polymer material through a complete revolution and to spread polymer on the entire upper inner surface of the vessel. The modified screw elements are used in combination with vertical polymer inlet nozzles which deposit incoming polymer directly on the ends of the elements as they pass beneath the nozzles.